Ammonium nitrate gas generator



United States Patent 3,126,304 AMMONIUM NITRATE GAS GENERATOR COMTOSITION Keith G. Penner and William G. Stanley, Seymour, Ind,

assignors to Standard Oil Company, Chicago, 111., a

corporation of Indiana No Drawing. Filed Aug. 27, 1962, Ser. No. 219,735

4 Claims. (1. 149-19) This invention relates to ammonium nitrate compositions suitable for use as gas generating materials having a relatively high burning rate, clean exhaust gases, and moderate flame temperature.

Ammonium nitrate based propellant materials are used for gas generation purposes where the exhaust gas from the combustion of the propellant is used to drive the turbine prime mover. The temperature of the exhaust gases (flame temperature) should be as low as possible [for the particular application in order to economize upon the type of metal used in the gas transfer lines or the amount of metal present to give a certain predetermined strength. In order to keep the gas transfer lines and the turbine chamber as free from deposits as possible, it is desired that the exhaust gases be clean, i.e., have a minimum of solid material present theerin. Gas generating compositions need to be storage stable for long periods and over wide ranges of atmospheric temperatures; this is especially true in the case of compositions intended for military use. It has been observed that even the alkali metal containing catalysts for the acceleration of the decomposition of ammonium nitrate produce some undesirable solid residues such as sodium carbonate and, therefore, it is desirable for many uses to have a low alkali metal containing catalyst content. On the other hand, many uses require a relatively high burning rate (inches per second at a given temperature and pressure) which burning rate is normally attained by using large amounts of such catalyst. It is the principal object of this invention to provide an ammonium nitrate composition particularly suitable for gas generator purposes which meets the above stringent requirements. Other objects of the invention will become apparent in the course of the detailed description thereof.

Broadly, the gas generator composition of the invention contains about 6-7% of cellulose acetate, about 89.4% of acetyl trie'thyl citrate, about 7.18 .4% of essentially pure dinitrophenoxyethanol, about 0.8-1.5 of alkali metal barbiturate combustion catalyst, about 4.56.4% of finely divided carbon, about 02-03% of ammonium oxalate, about 0.5l.5% of aromatic hydrocarbon amine gassing inhibitor, about 02-05% of N- phenylmorpholine, and the remainder essentially ammonium nitrate. An especially suitable composition consists of about 6.5% of cellulose acetate, about 8.8% of acetyl triethyl citrate, about 7.7% of pure dinitrophenoxyethanol, about 1% of sodium barbiturate, about of carbon black, about 0.2% of diammonium oxalate, about 1% of toluene diamine, about 0.2% of N-phenylmorpholine, and the remainder ammonium nitrate. (It is to be understood that all percentages set out herein are weight percent.)

The term ammonium nitrate as used in this specification and in the claims is intended to mean either C.P. grade or ordinary commercial grade ammonium nitrate or military grade. The particles may be coated with a small amount of moisture-resisting material such as petrolatum or parafiin. A minor amount of other inorganic nitrates such as sodium nitrate and/or potassium nitrate may be present. Finely ground ammonium nitrate is preferred.

The combustion catalyst utilized in the composition of the invention is an alkali metal salt of barbituric acid. The sodium barbiturate is preferred. The catalyst is present in the low amount of about 0.8-1.5% and usually about 1.0%.

The composition of the invention includes, as a cooling material, an ammonium oxalate, preferably diammonium oxalate, dispersed intimately throughout the binder material. The oxalate is present in the minor amount of about 02-03%.

The composition of the invention also includes N-phenylmorpholine, which may be the pure compound or commercial technical grade material, in an amount of about 02-05%.

The composition of the invention includes finely divided carbon as a burning rate accelerator in an amount of about 4.5-6.4% and more commonly 4.8-5.5%. The carbon component of the propellant composition includes finely divided, highly adsorptive activated carbons. These are well known in the art of decolorizing sugar and adsorption of gases. Examples of these are Norit and Nuchar, the former being a highly-adsorptive activated carbon used to adsorb odors, and to decolorize water, gases, chemical solutions, oils and greases. Nuchar is an activated carbon made from a residual organic material obtained in the manufacture of cellulose and is characterized by high porosity resulting in high adsorptive capacity. Like Norit it is used as a decolorizing and deodorizing agent.

Another general class of carbon useful for increasing the burning rate of the propellant composition are the carbon blacks. These are roughly classified as channel blacks prepared by the impingement of small natural gas flames, furnace combustion blacks producedf by the partial combustion of essentially gaseous hydrocarbons in closed retorts and furnace thermal blacks produced by thermal decomposition of hydrocarbons such as acetylene in preheated furnaces. The carbon blacks are characterized by low ash content by having extremely small particle size, that is, 50 to 5000 A., and contain adsorbed hydrogen and oxygen. Other carbon blacks which may be used in the propellant grains are lamp blacks produced by burning liquid fuels such as petroleum oils, tars and aromatic residues in specially designed pans, combustion taking place under restricted air supply conditions. The carbon blacks as indicated above are generally characterized by exceedingly small particle size, that is, well below #325 US. Standard sieve particle size. However, to avoid dusting and convenience in handling, some carbon blacks are formed to the so-called bead type carbon blacks which beads are generally of such dimensions as to pass through a #20 US. Standard sieve and are retained on a #200 US. Standard sieve. The beads are very soft and are physically unstable as beads and become disintegrated to smaller than #325 US. Standard sieve during the mixing and milling of the composited propellant components as described hereinbelow. The carbon blacks are of low ash content, and usually contain less than 0.5% ash. Examples of bead type carbon blacks are Micronex Beads (channel blacks) and Statex Beads (furnace blacks).

Yet another type of carbon which is useful for improving the burning rate of our gas-producing propellant composition is graphite, flake and amorphous. If derived from a natural graphite, the ash content should be reduced below about 5% which can be accomplished by treating the natural product by air flotation or the ash content may be reduced by leaching with mineral acid or by other methods well known to the art. We prefer graphite of colloidal or semi-colloidal particle size.

Still another type of carbon which has been found effective for increasing the burning rate of the gas-forming composition is finely ground petroleum coke, particularly petroleum coke obtained as a residue in the pipe-stilling of Mid-Continent heavy residuums. Such Patented Mar. 24-, 1964: v

coke usually contains les than about 1% ash and is preferably pulverized to pass through a #325 U.S. Standard sive prior to incorporation in the gas-producing propellant composition.

Ammonium nitrate compositions in general tend to develop gas in storage at elevated temperatures. The composition of the invention includes a gassing inhibitor component. Aromatic hydrocarbon amines when introduced into the ammonium nitrate based grain have the very desirable characteristic of decreasing the amount of gassing in high temperature storage; frequently they eliminate gassing for prolonged periods of time. The gassing inhibitors used here are illustrated by diphenylamine, dinapht'nylamine, phenyl naphthylamine. In the case of the naphthyl amines, the linkage between the naphthyl radical and the nitrogen may be either alpha or beta; and those amines represented by the empirical formula: RZ(NR'R") where Z is an aromatic nucleus selected from the class consisting of phenyl and naphthyl; R is selected from the class consisting of hydrogen and alkyl containing from 1 to 12 carbon atoms; R and R" are selected from the class consisting of hydrogen, and alkyl containing from 1 to 4 carbon atoms; and x is an integer from 1 to 3.

Examples of monoamine compounds are: aniline (monophenylamine, monoamino benzene), l-naphthylamine, toluidine (methylaniline) xylidine (dimethylaniline), dodecyl aniline, N-methyl aniline, N,N-dimetl1y1 aniline, N-sec-butyl aniline.

Examples of the diamine compounds are: diamino benzene (phenylene diamine), diamino toluene (toluene diamine), diamino naphthylene, methyl diamino naphthylene, dodecyl diamino naphthylene, i -secbutyl, diamino benzene, N,N-di-sec-butyl diamino benzene, and N-methyl diamino naphthylene.

Examples of triamine compounds are: triamino ben- Zeno, triamino naphthylene, triamino toluene, and triamino methyl naphthylene.

The matrix former or binder material utilized in the instant composition consists of cellulose acetate, acetyl triethyl citrate and dinitrophenoxyethanol.

The acetyl triethyl citrate is a well known plasticizer. The citrate may be the pure compound or commercial technical grade.

The dinitrophenoxyethanol component is the pure or essentially pure material; i.e., contains 5% of the bis- (dinitrophenoxy)ethane. In all cases, the dinitrophenoxyethanol is the predominant member and usually will represent 70% or more of this component. U.S. Patent No. 2,988,571 sets out a method of preparation of dinitrophenoxyethanol suitable for use herein.

The polymeric material present in the binder is cellulose acetate. Particularly suitable are the cellulose acetates which have combined acetic acid contents on the order of 50-58%. A preferred cellulose acetate is one made by Eastman Chemical Products, Inc, as Eastma 60.

The binder materials are present, based on the whole composition, of about 67% of cellulose acetate, about 53-94% of acetyl triethyl citrate, and about 7.1-8.4% of dinitrophenoxyethancl. The relative proportions of these components will vary within these ranges as determined by the specification requirements of the composition.

Illustration A generating composition was prepared by introducing the organic binder materials into a heated kettle provided with a mechanical stirrer; this composition is identified as Mark 4565. The binder materials were raised to a temperature Where they became a viscous homogeneous liquid. The catalyst and other additives were blended into the molten binder before the addition of the solid ammonium nitrate. During the blending of the ammonium nitrate, the temperature of the mixing operation was held below 130 C. In this instance, the ammonium nitrate was of a screen size: passing through a 14 number screen and retained by a 30 number screen; about 12% retained by a 80 number screen and passing through a 30 number screen; about 5% smaller than 80 number screen and the remainder larger than 14 number screen.

Data were obtained on burning rates at 70 F. and 1,000 p.s.i.a. by the Crawford Bomb Method. The approximate gas composition produced was obtained and the exhaust gas temperature calculated-attempts to measure exhaust gas temperature were subject to such lack of reproducibility as to be valueless for evaluation of dif ferences between compositions. The smokiness of the gas stream was noted. The composition here passed the military specification requirements.

Composition: Mark 4565 Ammonium nitrate 69.6 Cellulose acetate (Eastman-60) 6.5 Acetyl triethyl citrate 8.8 Dintrophenoxyethanol 7.7 Carbon black (Norite) 5.0 Sodium barbiturate 1.0 Toluene diamine 1.0 N phenylmorpholine 0.2 Diammonium oxalate 0.2

Exhaust gas temperature, F 2210 Burning rate, inches per second 0.130

Smoke None Specific impulse, seconds 184 Gas composition, mol percent:

CO 20.5 CO 9.5 H 22.3 H O 28.4 N 19.3

Thus having described the invention, what is claimed is:

1. A solid composition consisting of cellulose acetate, about 6-7%; acetyl triethyl citrate, about 89.4%; dinitrcphenoxyethanol, about 7.1-8.4%; alkali metal barbiturate catalyst, about 0.8-1.5%; finely divided carbon, about 4.5-6.4% ammonium oxalate, about 0.2-0.3%; aromatic hydrocarbon amine gassing inhibitor, about 0.5-1.5%; N-phenylmorpholine, about 0.2-0.5% and the remainder of said composition being essentially ammonium nitrate.

2. The composition of claim 1 wherein said gassing inhibitor is toluene diamine.

3. The composition of claim 1 wherein said catalyst is sodium barbiturate.

4. A solid composition consisting of cellulose acetate, about 6.5%; acetyl triethyl citrate, about 8.8%; dinitrophenoxyethanol, about 7.7%; sodium barbiturate, about 1%; adsorptive activated carbon, about 5%; diammonium oxalate, about 0.2%; toluene diamine gassing inhibitor, about 1.0%; N-phenylmorpholine, about 0.2%; and the remainder of said composition being ammonium nitrate.

No references cited. 

1. A SOLID COMPOSITION CONSISTING OF CELLULOSE ACETATE, ABOUT 6-7%; ACETYL TRIETHYL CITRATE, ABOUT 8-9.4%; DINITROPHENOXYETHANOL, ABOUT 7.1-8.4%; ALKALI METAL BARBITURATE CATALYST, ABOUT 0.8-1.5%; FINELY DIVIDED CARBON, ABOUT 4.5-6.4%; AMMONIUM OXALATE, ABOUT 0.2-0.3%; AROMATIC HYDROCARBON AMINE GASSING INHIBITOR, ABOUT 0.5-1.5%; N-PHENYLMORPHOLINE, ABOUT 0.2-0.5%; AND THE REMAINDER OF SAID COMPOSITION BEING ESSENTIALLY AMMONIUM NITRATE. 